The present invention is related to optical communication systems and, more particularly, to optical backplanes associated with communicating information between components of a computer system and communicating multiple optical signals in telecommunication networks.
The current generation of computers is often limited by the speed at which information can be transmitted between electronic components such as processors and memory chips. For example, a typical personal computer bus or motherboard operates at a frequency of only 100 MHz, whereas processors are often able to reach speeds of 1 GHz. Similarly, logic circuits frequently outpace inter-board interconnect speeds within subsystems which depend on communications between cards within a computer. Development of technologies for communications within computer systems to replace conventional passive backplanes and motherboards is a long standing goal to achieve higher data throughputs. Under current conditions, bus traffic generally increases as computing power of a processor increases. Therefore, limited bus bandwidth associated with many computer systems represents a major bottleneck to efficient communications between board-to-board data interfaces.
There are two major types of optical backplanes: free space and guided wave. Free space optical backplane bus system generally has free space channels and diffractive optical elements to direct associated signal beams. Guided wave optical backplanes generally include optical beams traveling through total internal reflection within an associated waveguiding plate. DOEs such as holographic gratings are frequently used as beamsplitter/deflectors in guided wave optical backplanes.
Difficulties have been noted in both types of optical backplane with obtaining uniform optical signal power levels at the respective outputs. Uniform intensity of output optical signal power levels is difficult to obtain even when diffraction efficiencies of associated DOE""s has been optimized in a prior guided wave optical backplanes.
Optical backplanes typically include one or more optical signal input ports and one or more optical signal output ports. Incoming optical signals are monitored at each input port. The optical signal is generally directly coupled to an optical backplane which routes the signal to another unit or component associated with the optical communication system. One example of such components includes optical cross connect fabric, optical switches, wavelength division multiplexers and/or demultiplexers. Optical backplanes often provide a cost effective and compact solution for many optical communication systems.
In accordance with teachings of the present invention a method and apparatus are disclosed for broadcasting and rebroadcasting optical signals to multiple components of a computer system. One aspect of the present invention includes an optical backplane assembly for communicating optical signals with multiple components based on guided wave interconnects. The invention may be implemented with holograms and active optical elements providing interfaces between a conventional electrical backplane with attached components such as circuit boards and an optical backplane. One embodiment includes a distributor installed as a center component having a receiver, a doubly multiplexed hologram, and a transmitter. Any signals coming from one of the components may be collected by the receiver of the distributor and rebroadcast from the transmitter of the distributor to all of the other components.
A further aspect of the present invention includes an optical bus assembly with very high data throughput capability as compared with conventional passive busses and backplanes. The optical bus assembly preferably includes bidirectional signal paths to both receive and transmit optical signals between a plurality of components such as circuit boards. Active couplers formed in accordance with teachings of the present invention may both receive and transmit optical signals. Each active coupler may include active optical elements such as an optical signal transmitter and an optical signal receiver. Each active coupler may also include a hologram or holographic optical element which functions as an optical signal beam splitter and an optical signal deflector.
Technical advantages of the present invention include increased bandwidth capacity, increased speed, reduced cross talk and reduced interference during communication of optical signals between various components of a computer system or a communication system. Additional components may be added to an optical backplane assembly formed in accordance with teachings of the present invention without substantially decreasing associated bandwidth capacity or speed of data communication between components and without a significant increase in cross talk or interference during communication of optical signals between the components. The number of slots or electrical connections associated with the optical backplane assembly may be substantially increased without reducing overall performance characteristics of the optical backplane assembly and attached components.
An optical backplane assembly formed in accordance with teachings of the present invention may use existing slots or electrical connections associated with presently available electrical backplanes and existing electrical circuit cards or any other component. Both initial assembly and later modification of the optical backplane assembly may be easily accomplished by directly connecting components with the conventional electrical backplane. Any component coupled with an optical backplane assembly formed in accordance with teachings of the present invention may transmit and receive data or information from all other components coupled with the optical backplane assembly. Also, components may be inserted or removed from the optical backplane assembly without limiting or restricting communication between other components coupled with the optical backplane assembly.
Another aspect of the present invention includes an optical backplane assembly with a distributor operable to switch optical signals in large optical communication or telecommunication networks. The distributor is preferably located adjacent to a midpoint in the optical backplane assembly. The distributor may receive optical signals from other components attached to the optical backplane assembly, switch the optical signals, and rebroadcast the optical signals to the other components.
An optical backplane assembly with a central distributor formed in accordance with teachings of the present invention provides substantial advantages as compared to prior guided wave and free space optical backplane systems used for broadcasting signals. These advantages include equalized fan-out power or output power, increased interconnect distance, and simpler fabrication. The distributor with active optical elements allows doubling associated interconnect distances as compared to many prior optical backplanes. The present invention reduces the total number of diffractive optical elements such as single holograms and doubly multiplexed holograms required to produce an optical backplane assembly. The number of fabrication and assembly steps is also reduced.